Pipe or duct insulation is used in a variety of applications, such as in residential, industrial and commercial applications. Insulation may be made of inorganic materials like fiberglass, calcium silicate, and mineral wool, as examples. Inorganic type insulation can be used for high temperature applications. Insulation may be made of polymeric foam materials like polyurethane, polyisocyanurate, polystyrene, polyolefin, and synthetic rubber, as examples. Polymeric foam type insulation is commonly used for medium and low temperature applications. Aerogel material has been demonstrated to provide superior insulation properties, but aerogel material is expensive. With the increasing importance of energy efficiency, thick-wall pipe insulation is in high demand.
Polymeric foam insulation can be rigid or flexible. The rigid foam can be put on a destination pipe by either in-situ casting (i.e., spraying foam inside a jacket and letting it cure to solidify) or by assembling pre-formed pieces such as semicircular-shaped profiles, which are cut from a big foam block/plank. Flexible foam can be a foam sheet (i.e., single-layer or multi-layer, which is produced from an extrusion process and tailored to a specific size to cover a destination pipe) or a foam tube, which is extruded from an annular die and then opened via a slit to allow a pipe to get in. In order to make foam insulation for a pipe with a large outer diameter (OD), be it either a foam sheet or a foam tube, a large-capacity extruder and corresponding large-capacity downstream cooling device can be used, both of which require large capital investment. In addition, high extruder throughput makes uniform cooling of polymer melt and foam more difficult. Therefore, it is highly desirable to manufacture a foam product used for large-diameter pipe insulation without the use of a large extruder.
In addition, thermal contraction of insulation material is also a challenge for pipe insulation, especially for cryogenic applications. For example, for cryogenic applications, the temperature of the insulation may become low during use, although the insulation is normally installed at a higher ambient temperature. The insulation material tends to compress or shrink when its temperature drops, which may lead to separation between insulation sections. The resulting gap can lead to condensation of water vapor inside the insulation or between the insulation and the pipe, causing serious damage to the insulation. Likewise, a pipe or duct can thermally expand along its length which may lead to separation between insulation sections and cause gaps that can lead to condensation of water vapor inside the insulation or between the insulation and the pipe and cause serious damage to the insulation.
Further, polymer insulation materials show higher thermal expansion/contraction coefficient than inorganic insulation materials. Among those polymer insulation materials, economic low density polyethylene (LDPE) demonstrates particularly poor thermal contraction. In addition, closed-cell, low-density, flexible polymeric foam shrinks more than rigid or high-density foam. Hence, it would be advantageous to compensate for the thermal contraction of the polymer foam insulation such that no gap (or separation) would develop at joints due to temperature changes. However, large diameter pipe insulation, for example rigid semicircular foam, may require a lot of space to store in a truck or in a warehouse, which makes shipping and storage inefficient. Finding a more efficient method of shipping and storing large diameter pipe insulation is a challenge.
In addition, variations in pipe dimensions can make installation of pipe insulation difficult. Usually, insulation material is sized to fit a pipe's OD. For example, in the case of a pipe joint, for example, the OD changes for a short distance due to either a larger OD adapter sleeve or one end of a pipe being slightly enlarged to overlap another pipe. Thus, the insulation should be changed or varied accordingly. Otherwise, there could be a gap left in the insulation and that gap would be very problematic. For a cryogenic insulation application, a gap may expose the pipe to the outer environment, and thereby allow water vapor to enter through the gap. The water vapor may result in condensation within the insulation or between the insulation and the pipe. This moisture may cause serious damage to the insulation system and require the system to be replaced after several heating-cooling cycles.
A vacuum method is an effective way of insulation in terms of heat conduction. However, the vacuum method is relatively expensive. Air insulation is less efficient than vacuum insulation. Air is a good insulation medium with thermal conductivity about five (5) times less than most plastics and one thousand (1,000) times less than steel. Ideally, air alone would be used as insulation since there is not additional material cost. However, heat transfer takes place not only from thermal conduction but also from convection and radiation. If air is allowed to move freely over a pipe surface, heat transfer from convection would be much more significant than that from conduction. One solution to reduce heat convection from air flow is to get air sealed inside insulation such as in the form of foam (i.e., many air bubbles) or sealed in a hollow profile (i.e., one big bubble).
Embodiments disclosed herein can address some or all of the issues mentioned above, including (1) how to make insulation for large diameter pipes or ducts by using a relatively small extruder, (2) the capability to adapt pipe or duct dimension variations so the insulation installation is easy and insulation would not be too tight or too loose on a pipe, (3) addressing thermal contraction of flexible polymeric foam material, (4) shipping and storing efficiency, and (5) utilizing air as a free insulation medium.